<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .active{
      color: red;
    }
  </style>
</head>

<body>
<div id="app">
   <ul>
     <li v-for="(item ,index) in movies"
         v-bind:class="{active:currentIndex === index}"
         @click="changeIndex(index)">
          {{index+1}}.{{item}}
     </li>
   </ul>
</div>


<script src="../js/vue.js"></script>
<script>
    const app = new Vue({
        el:'#app',
        data:{
            movies:['海王','海贼王','海尔兄弟','加勒比海盗'],
            currentIndex:0,
        },
        methods:{
            changeIndex(index){
              this.currentIndex = index
            }
        }
    })
</script>
</body>
</html>